This application is a 371 of PCT/EP02/05010 filed May 7, 2002.
This invention relates to additives for the permanent internal hydrophilicization of polyolefin-containing materials, preferably polypropylene fibers.
In many cases, the surface of plastic products has to be provided with special effects which either can only be produced incompletely, if at all, during molding for technical reasons or can only be produced unfavorably for economic reasons. One such effect, for example, is the improvement of wettability with polar liquids, such as water. Technical applications in this respect include, for example, the production of hygiene articles.
In the production of hygiene articles, such as diapers or sanitary napkins, and also wiping cloths or “geofleeces”, absorbent materials are used to take up aqueous liquids. In order to prevent direct contact with the absorbent material during wear and to increase wearing comfort, this material is enveloped in a thin water-permeable nonwoven. Such nonwovens are normally made from synthetic fibers, such as polyolefin or polyester fibers, because these fibers can be inexpensively produced, show good mechanical properties and are heat-resistant. However, untreated polyolefin or polyester fibers are not suitable for this application because they are not sufficiently permeable to water-containing fluids on account of their hydrophobic surface.
In principle, the fibers can be given the necessary hydrophilic properties by subsequent coating with corresponding finishes (external additives) or can be made sufficiently hydrophilic by the incorporation of suitable additives (internal additives) during their production. The second of these two options is described in WO 95/10648 which discloses diesters of polyethylene glycol with fatty acids or derivatives thereof as suitable permanent additives. In the Examples, reaction products of oleic acid with polyethylene glycol having a molecular weight of 400 are described as particularly advantageous. Applicants' hitherto unpublished DE 100 155 54 describes reaction products of two parts lauric acid with polyethylene glycols which are suitable as internal additives for hydrophilicizing polyolefin fibers.
Additives such as these are generally processed with polyolefin granules to form a masterbatch which is then added as such to the polymer granules before processing to the fibers or other end products, followed by extrusion. However, it is desirable for reasons of cost to be able to incorporate such additives during the actual extrusion process in the extruder. Unfortunately, attempts to incorporate known additives by direct addition have been frustrated by problems attributable to the low-temperature stability of the additives. The compounds have cold cloud points above 20° C. Accordingly, when they are incorporated by direct addition, the compounds crystallize out and block the dies.
Accordingly, the problem addressed by the present invention was to provide additives for the permanent hydrophilicization of polyolefin fibers which would not have any of the disadvantages mentioned above. These additives would be capable of providing the fibers or products with sufficient hydrophilia which they would retain even under stress, for example after the repeated wetting with water which they undergo in washing processes.